Pulverized coal feeding and pressurizing system



July 1, 1958 A. B. HALE ETAL PULVERIZED com. FEEDING AND PRESSURIZINGSYSTEM Filed Aug. 27. 1953 uzmci .ww mmtimzh umuta 538E INVENTORS ARLANB. HALE MILFRED L. BROWN STANTON E. PARRISH B 4 2 ATTORNE PULVERIZEDC(DAL FEEDING AND PRESSURIZENG SYSTEM Asian B. Hale, St. Alhans,Milfretl L. Brown, Nitro, and Stanton E. Parrish, South Charleston, W.Va assrgnors to Union Carbide Corporation, a corporation of New YorkApplication August 27, 1953, Serial No. 376,944

3 Claims. (Cl. 110-404) This invention relates to a process andapparatus for introducing pulverized coal at atmospheric pressure into astream of oxygen under pressure.

As part of an overall process of coal gasification, a fluidized mixtureof coal and oxygen is fed into a reactor. In order to provide such amixture, it was necessary to devise a process and apparatus fordelivering a steady stream of free flowing coal, from a source of coalat atmospheric pressure, into a stream of oxygen gas at pressures up tofive pounds per square inch gauge. Under such a pressure, the coal andoxygen are mixed in a vessel operating on the fluidized solids principleto produce a mixture having the characteristics of a fluidized solidwhich can then be delivered at high velocity into a reactor.

In order for the fluidizing vessel to operate properly in mixing thecoal and oxygen, it must receive a steady flow of free flowing coalwhich is at a slightly higher pressure than the pressure under which theoxygen is introduced into the fiuidizing vessel, or fluidizer. If thispressure differential is not maintained with the higher pressure on thecoal side, the oxygen will blow back and force the coal back into thesupplying mechanism 'with an explosion the probable result. Thus, thepressure on the coal side must be immediately responsive to any changesor surges in the oxygen, both to insure proper mixing of the coal andoxygen and to prevent explosion.

We have discovered a method and apparatus for introducing the coal intothe fiuidizer, while controlling the pressure with carbon dioxide orother inert gas, by employing automatically controlled valves in such amanner that the coal is delivered at a steady rate into the fluidizingchamber and any change in the pressure of the oxygen coming in isimmediately and automatically compensated for by a corresponding changein the pressure of the carbon dioxide or other inert gas on the coal inthe coal chamber from which it is conveyed to the fluidizer.

The invention will be described in detail by reference to theaccompanying drawing which illustrates an apparatus embodying theinvention.

The drawing is a partially sectioned view of the apparatus.

In the drawing is shown a coal supply hopper where the pulverized coalwhich is to be processed is stored at atmospheric pressure. From thesupply hopper, the coal is delivered through communicating means, inthis case a rotary feeder 12, into a pressurized chamber, herein calledthe coal chamber 14, which is under pressure. In order that the pressureof the weight of the coal itself in the coal chamber may be keptconstant, a relatively uniform quantity of coal is maintained in thecoal chamber by means of a diaphragm operated switch 16 which isresponsive to the level of the coal. The switch 16 is connected throughwires 19 to a relay 20, through which it controls the motor 22 whichrotates the rotary feeder 12. When the coal level in the coal J TnitedStates Patent 0 chamber 14 falls below a predetermined minimum level,the pressure of the coal on the diaphragm switch 16 lessens and themotor 22 is actuated, causing the rotary feeder 12 to deliver more coalfrom the supply hopper 10 into the chamber until the maximum level isreached and there is again sufficient coal pressure on the switch 16 tohalt the motor 22.

The coal at the bottom of the coal chamber 14 is picked up by meanscommunicating between the coal chamber 14 and the fiuidizing chamber 30,which in the embodiment shown comprises a constant pitch screw 24revolving in a cylinder 38 and driven at a low constant speed by a motor26 through reduction gears 28. The screw 24 is relatively tight againstthe walls of the cylinder 38 in order to prevent coal being blown backthrough the screw. The feed screw 24 delivers the pulverized coal intothe fluidizer chamber 30. Oxygen is admitted to the fiuidizer 30 throughan inlet 32 at the bottom and moves up through the chamber, picking upthe pulverized coal delivered by the feed screw 24. In the fiuidizer 30,the pulverized coal and oxygen form a mixture having the properties of afluidized solid and leave the fluidizer in that form through one or moreexit pipes 34. A rupture disk 36 is provided in the fiuidizer as asafety precaution against any accidental build-up of a pressure ofexplosive force.

A pressure differential between the fiuidizer and coal chamber isregistered through interconnecting pipes between a pressurediifere'ntial transmitter 54 and a port 64 in the fiuidizer and a gasport 50 in the coal chamber. A pipe 62 connects the fiuidizer port 64 toone side of the pressure differential transmitter 54, thus allowing theoxygen pressure from the fluidizer to afiect the transmitter. The otherside of the pressure differential transmitter is connected to the coalchamber port 50 by the pipe 60, whereby the pressure in the coal chamber14 afiects the transmitter 54. Instrument air is supplied to thepressure differential transmitter 54 through instrument air conduit 78.The pressure differential transmitter 54 is responsive through adiaphragm to the difference between the pressure in the fiuidizer 30 andthe pressure in the coal chamber 14 and as this difference in pressurechanges the transmitter 54 proportionately varies the pressure ofinstrument air which it permits to How through the tubing toa pneumaticrecorder-controller 82. The pressure differential transmitter used inour embodiment of the invention was a Republic Pneumatic PressureTransmitter, model P-0308, manufactured by the Republic Flow MetersCompany, of Chicago,

Illinois.

As the pneumatic recorder controller 82 receives varying pressures ofinstrument air from the transmitter 54 corresponding to variances in thepressure differential between the fluidizer 30 and the coal chamber 14it records the pressure differential on a graph. When the pressuredifferential falls below or exceeds present limits the controller 82acting on a source of instrument air supplied through instrument airconduit 84, operates one or the other of the two motor valves 68 and 42by regulating the flow of air through conduits 66 and 70, therebycontrolling the supply of carbon dioxide or other inert gas into or outof the coal chamber 14. The pneumatic controller used in our embodimentof the invention was Foxboro Pneumatic Recorder-Controller, model 40,manufactured by the Foxboro Company, of Foxboro, Massachusetts. Thepressure differential transmitter 54 and the pneumatic controller 82,together with the motoroperated valves 42 and 68, an instrument airsupply and the necessary connecting conduits, comprise a control meansfor maintaining a difierence in pressure between the fiuidizer 30 andvthe pressurized coal chamber 14,'

We have found that a pressure in the coal chamber 14 about one inch ofwater above that in the fluidizer is preferable. When the oxygenpressure in the fluidizer 30 increases, so as to require a highercorresponding pressure in the chamber 14 to maintain the necessarydifferential, the controller 82 acts through line '70 to open the motorvalve 42, thereby allowing the inert gas to flow into the coal chamber14 through the port by means of pipes 44,46 and 48 until the necessarypressure is built up in the.chamber 14, whereupon the valve 42 closesagain.

When the pressure in the fluidizer 30 begins to fall below the maximumdifferential with the pressure in the coal chamber 14, the controller 82works through line 66 to open a motor valve 68 which allows inert gas toleave the chamber 14 through the port 50 and pipes 48, 46 and 76, untilthe pressure in the chamber is reduced to the proper level, whereuponthe valve 68 closes again.

In the event that the oxygen pressure in the fluidizer 30 was loweredvery suddenly, a large quantity of coal would be forced into thefluidizer before the controller 82 and valve 68 could cooperate toreduce the pressure in chamber 14. To prevent this from happening, thechamber An additional advantage of the invention is the provisionagainst any extreme downward fluctuation in the oxygen supply pressure.The direct line between the coal chamber and fluidizer, with a checkvalve in it, serves to rapidly equalize the pressures in such a case,and prevents the coal from being forced through the screw feeder toorapidly.

Equivalents of some individual elements of the invention can besubstituted within the spirit of the invention. For instance, a conveyorbelt or drag conveyor, if sufficiently enclosed, might be used in placeof the screw feeder shown, and another type of switch responsive to thelevel of the coal in the'coal chamber might be substituted for thediaphragm-operated switch as shown.

While the elements of the invention have been described and detailedwith respect to specific embodiments,

14 and fluidizer 30 are connected by pipes 48 and 72,

pipe 72 having in it a check valve 74. In the event of a sudden andexcessive drop in the oxygen pressure in the fluidizer resulting in apressure difierential of more than five inches of water, valve 74.0pensand permits the inert gas to flow directly from the coal chamber 14 tothe fluidizer 30, thus rapidly restoring the proper differential inpressure between the two chambers.

The apparatus has proven highly successful in operation and has provideda constant and uninterrupted supply of a fluidized mixture of coal andoxygen in the proper proportions. The coal supply can be readily renewedby simply leading coal at atmospheric pressure into the open-top supplyhopper. There is no problem of batch loading through pressure tightdoors; the rotary feeder provides the necessary pressure tight seal. Therotary feeder operates intermittently, as controlled by the diaphragmoperated switch, and at very low speeds, five to seven revolutions perminute having been found ample. This low speed means low wear on'thefeeder and cooperating parts'and hence low maintenance costs.

Because the pressure differential is maintained by an automatic controlmeans controlling the inert gas pressure, there is no opportunity for asudden oxygen pressure build-up to force the coal back against the feedscrew. Therefore, the feed screw can be of constant pitch, that isnon-compressive and non-tapered in design, and can rotate at relativelylow speed. Previously, when it was desired to feed a granular materialagainst a pressure, it was customary to make the screw feed compressivein design and rotate it at high speeds. This meant that the granularmaterial compacted at the smaller delivery end of the screw. While sucha design does resist blow back pressures to some extent, it results inan undesirable lumpy deaerated feed and high abrasive wear on theworking parts, causing excessive maintenance problems and expense. Thus,the screw feed of the invention has the advantage of delivering freeflowing coal, as Well as that of operating with low abrasion and at lowspeed, thereby greatly reducing maintenance problems.

For the successful operation of the invention, it is necessary tocontrol the differential pressure across the screw feeder, between thefluidizer and the coal chamber, at a value not exceeding one inch ofwater. Differentials greater than this tend to cause excessivevariations in the 'rate of coal feed. Such control has been madepossible by the use of the motor valves, controlled by the pneumaticcontroller, to regulate the flow of inert gas in and out of the coalpot, and thus the pressure in the coal pot. This system compensates forall normal variations in the pressure of the oxygen supply.

it is to be understood that the substitution of equivalents for specificelements of the invention will not constitute a departure from the truespirit and scope of the invention as claimed.

We claim:

1. An apparatus for continuously forming under pressure an oxygen andpulverized coal mixture having the characteristics of a fluidized solid,comprising a closed fluidizing chamber having at least one outlet forsaid mixture and an inlet for oxygen; a pressurized coal chamber havinga gas port for admitting inert gas into and out of said chamber; meanscommunicating between said coal chamber and said fluidizing chamber forconveying pulverized coal under pressure from said coal chamber intosaid fluidizing chamber; an open pulverized coal hopper adjacent to saidcoal chamber for receiving and storing pulverized coal at atmosphericpressure; means communicating between said coal hopper and said coalchamber for conveying pulverized coal from said coal hopper into saidcoal chamber; means responsive to the level of coal in said coal chamberand controlling said communicating means from said coal hopper into saidcoal chamber so as to maintain a constant predetermined level ofpulverized coal in saidcoal chamber; and control means for controllingthe pressure in said coal chamber relative to the pressure in saidfluidizing chamber by regulating the flow of an inert gas into and outof said coal chamber through said gas port so as to maintain thepressure in said coal chamber above the pressure in said fiuidizingchamber by a predetermined value.

2. An apparatus in accordance with claim 1, wherein said .meanscommunicating between said coal chamber and said fluidizing chamber forconveying pulverized coal from said coal chamber to said fiuidizingchamber comprises a rotating, constant pitch, constant speed screw feedmechanism.

3. An apparatus in accordance with claim 1, wherein said meanscommunicating between said coal hopper and said coal chamber forconveying pulverized coal from said hopper to said coal chambercomprises a rotary feeder means having an inlet and an outlet, andpressure sealing means between said inlet and said outlet.

4. An apparatus in accordance with claim 3 wherein said means responsiveto the level of coal in saidcoal .chamber and controlling said rotaryfeeder means comprises a motor driving said rotary feeder means andelectric circuit control means for said motor comprising a pressureresponsive switch positioned within said coal chamber responsive to thelevel of coal therein, operable to periodically actuate said motor tocause the operation the level of pulverized coal in said coal chamber,and said switch controlling a driving means rotating said rotary feeder.

6. An apparatus in accordance with claim 1, additionally comprising arelief conduit communicating between said coal chamber and saidfiuidizing chamber having therein a check valve, said check valveregulated so as to open automatically when the pressure in said coalchamber exceeds the pressure in said fluidizer by a predetermined valueand to remain open until the pressure in said coa-l chamber no longerexceeds the pressure in said fluidizer by more than a predeterminedvalue.

7. An apparatus in accordance with claim 1, additionally comprising arupture disk positioned in the wall of said fluidizer chamber, saidrupture disk being of such strength that it will rupture when thepressure in said fluidizer exceeds a predetermined value.

8. An apparatus in accordance with claim 1, wherein said control meansfor controlling the pressure in said coal chamber with respect to thepressure in said fluidizing chamber comprises an oxygen conduitconnecting said fiuidizing chamber to a pressure differentialtransmitter; an inert gas conduit connecting said coal chamber gas portto said pressure diiferential transmitter; a motor operated valvepositioned in an inlet conduit conveying inert gas from an outsidesource into said coal chamber through said gas port and responsivethrough an instrument air control conduit to said pneumaticrecorder-controller, said motor operated valve opening by the action ofsaid pneumatic recorder-controller when the pressure in said coalchamber falls below the pressure in said fiuidizing chamber by apredetermined value and said valve being held open by the action of saidpneumatic recorder-controller until the pressure in said coal chamberagain exceeds the pressure in said fluidizer chamber by a predeterminedvalue; a second motor operated valve positioned in an outlet conduit forexhausting inert gas from said coal chamber through said gas port, saidsecond motor operated valve being responsive through an instrument airconduit to said pneumatic recorder-controller, said motor operated valveadapted to open by the action of said pneumatic-recorder controller whenthe pressure in said coal chamber exceeds the pressure in saidfluidizing chamber by more than a predetermined value and said valveadapted to remain open by the action of said pneumaticrecorder-controller until the pressure in said coal chamber no longerexceeds the pressure in said fluidizer by more than said predeterminedvalue.

References Cited in the file of this patent UNITED STATES PATENTS May etal Nov. 10, 1953

